1. Field of the Invention
The invention relates to a data transfer system for transferring data between two function circuits which operate synchronously with different clock frequencies.
2. Description of the Related Art
Ordinarily, a data processing apparatus such as a computer is constituted by a plurality of circuits and units. Proper operating frequencies are set into those circuits in accordance with their operating characteristics, respectively. Specifically speaking, the data processing apparatus has a plurality of frequency dividing circuits each for generating a frequency-divided clock by frequency-dividing a source clock and supplies the frequency-divided clock of the proper operating frequency every circuit. In the case, although the circuit operates at the different operating frequency every circuit, in the case of transmitting and receiving data between the two circuits which operate at the different operating frequencies, it is necessary to properly adjust transmission and reception timing.
As an method for adjusting the transmission and reception timing, a method is known in which transmitting and receiving of data is performed by using timing at which leading edges or trailing edges of two clock signals having the different operating frequencies coincide. For example, Japanese Patent Kokai No. 10-303874 (Patent Literature 1), discloses a sync edge detecting system at the time of transferring data between two circuits which operate synchronously with two clock signals having different frequencies. According to this system, sync signals SYNCa and SYNCb are generated at timing when edges of two clock signals CLKa and CLKb and the data transfer is performed by using the sync signals.